In the art of torque wrenches, there is that special class of wrench which includes means for indicating (to the operator of the wrench) when a set predetermined force is transmitted by the wrench onto a related piece of work. More particularly, the class of wrench noted above and with which the present invention is concerned is an adjustable click-type torque wrench which is such that when a predetermined set force is transmitted by it onto a piece of work, certain parts within the wrench move rapidly from a normal position to an actuated position in a manner so that a slight movement, impact and an audible click-like sound are transmitted through the wrench to signal the operator that a predetermined set force has been reached.
Ordinary torque wrenches of the specific class here concerned with include elongate, tubular lever arms with front and rear ends, hand grip means at the rear ends of the arms and work-engaging heads at the front ends of the arms. The heads have elongate cranks projecting rearwardly and freely into and through the forward portions of the lever arms. The forward portions of the cranks are pivotally mounted to the forward ends of the arms and have flat, rearwardly disposed seats at their rear ends. Within the lever arms, rearward of the cranks, are longitudinally shiftable blocks with flat, forwardly disposed seats. Cam blocks with flat front and rear faces are engaged with and between the seats on the cranks and blocks. Within the lever arms, rearward of the blocks, elongate, axially extending compression springs are arranged to engage the blocks and to normally yieldingly urge the blocks forwardly toward the cranks, with the cam faces in pressure engagement with the crank and block seats. Within the rear end portions of the lever arms and engageable at the exteriors thereof are manually operable setting means which engage the springs and are operable to compress and vary the amount of force exerted by the springs onto and through the noted blocks.
In operation of the above noted class of wrenches, when a sufficient actuating force is exerted between the lever arms and the heads, as by manually applied force on the lever arms (when the heads are in stop engagement with related pieces of work) the rear ends of the cranks pivot laterally in the lever arms and strike the inner adjacent sides of the arms to transmit audible clicking sounds. When the cranks swing laterally, the cam blocks turn or rock between their related seats. Such rocking of the cam blocks urges the slide blocks rearwardly against the resistance of the springs.
The flat, front and rear faces of the cam block have straight edges on planes parallel with the pivotal axis of the cranks. The seats with which said faces of the cam blocks are related have shoulders, against which the noted edges of the cam blocks stop and are pivotally supported.
The lateral extent of the cam faces and the axial or longitudinal extent of the cam blocks determine the stability of the cam blocks between their related seats. The dimensions of the cam blocks and their resulting stability in such wrenches is not subject to change or variation.
It will be apparent that the magnitude of the actuating force in wrenches of the character described above is determined by the length of the mechanical advantage afforded by the cranks, the stability of the cam blocks and the pressure exerted by the springs. By adjusting the pressure of the springs, the actuating forces can be varied and set (within limited ranges of forces) as desired.
In one notable and special adjustable click-type wrench, an elongate link with front and rear ends is arranged in the lever arm between the arm and the slide block. The front end of the link is pivotally connected with the rear end of the crank and the rear end of the link is formed with a rearwardly disposed seat with which the cam block is engaged. The link is pivotally supported in the lever arm, intermediate its ends, by a pivotal support ring engaged about the link and which has a spherical exterior surface pivotally slidably engaging the interior of the lever arm. The support ring is shiftable longitudinally of the link and can be set in desired position longitudinally thereof. The pivot link imparts mechanical advantage to the spring of the wrench, enabling the use of a rather light spring. By adjusting the longitudinal position of the support ring on the link, fine adjustment of the wrench for operating through several different ranges of forces, without changing the spring, is possible. When this wrench structure is operated, the crank and the rear end of the link strike the interior surface of the lever arm.
The above noted special adjustable click-type wrench is disclosed in U.S. Pat. No. 3,772,942, issued Nov. 20, 1973, and entitled "Adjustable Torque Wrench".
The manually operable setting means for click-type wrenches provided by the prior art characteristically include plugs within the rear end portions of the lever arms rearwardly of the springs therein. The plugs have threaded apertures through which elongate threaded bolts or screws are engaged. Cylindrical spacer and washer assemblies, slidably engaged in the lever arms, are arranged between the screws or bolts and their related springs. By advancing the screws forwardly and rearwardly in their related plugs, the extent to which the springs are biased axially and the force exerted thereby onto and through the cam blocks of the wrenches is adjusted to set the operating forces of the wrenches.
In addition to the above, and to adjust the wrenches to operate at predetermined forces, various manually engageable rotatable and axially shiftable parts, with calibrations and/or scales, are cooperatively related with the screws and the lever arms to facilitate rotation and axial adjustment of the screws to desired positions. The calibrations or scales are provided and function to translate the axial positioning of the screws and the degree to which the springs are biased thereby, into operating forces.
In most wrenches provided by the prior art, the elongate tubular metal lever arms are formed with various splines, grooves, channels and openings which must be established therein by various costly to perform machining operations. Further, the lever arms of such wrenches, after all necessary machining and forming operations are performed thereon, must be heat treated or case-hardened to, for example, 61 Rockwell (inside and outside) to make them sufficiently strong and durable for their intended use. Still further, after machining and heat treating the lever arms, it is customary and necessary to clean all surfaces of the arms and to electroplate all of the exposed surfaces thereof with bright chrome or the like, to protect those surfaces and to make the wrenches marketable. (To the best of my knowledge and belief, all distributors and purchasers of torque wrenches of the class here concerned with require that the lever arms be clean, bright and protected with chrome-plate).
In practice, in torque wrenches of the general class here concerned with, the noted internally threaded plugs set within the lever arms, which plugs serve to carry the screws of the wrench adjusting or setting means, are set within the arms by staking or otherwise forming the walls of the arms radially inwardly into tight locking engagement in grooves or the like, formed in the exteriors of the plugs. Accordingly, the plugs must and are commonly set within the arms of the wrenches prior to heat treatment and chrome plating thereof. While the foregoing appears to be a good and straightforward manufacturing procedure, it has been found to have created several serious problems which have not been satisfactorily corrected or overcome by any one of numerous costly procedures which have been practiced in efforts to solve or correct those problems.
One notable serious problem is the tendency for the arms to be soft and/or weak at and adjacent to the plugs therein and to warp or otherwise distort during heat treatment. The existence of soft or weak portions in the arms and distortion thereof is brought about by the fact that the presence of the plugs in the arms, which plugs are of substantial mass and mask off their adjacent inside surfaces of the arms, prevent proper quenching of the masked portions of the arms, and, as heat storing elements, result in slowed and uneven quenching and coating of the portions of the arms adjacent thereto, during heat treatment thereof. As a result of the foregoing, the interior surfaces of the arms adjacent the plugs are not case-hardened during heat treatment and the hardening of the exterior surfaces at and near the plugs is generally less than and varies notably from the remaining portions of the arms.
Other serious problems are brought about by the fact that the interior surfaces of the lever arms of such wrenches tend to be covered and ladened with scale and rust which adversely interferes with the free sliding and/or pivotal movement of the several elements and/or parts of the wrench structures which occur within and contact the interior surfaces of the arms and/or the operation of which is subject to being adversely interfered with by loose scale, rust and other contaminants which come into contact therewith.
The scale and rust on the interior surface of the lever arms of such wrenches results from the fact that in the course of chrome plating the lever arms, uniform and satisfactory plating of the interior surfaces thereof cannot be effected. This is due in part to the collecting and trapping of gases in the arms, during plating. The trapping of gases is caused by the plugs which are set or fixed within the arms prior to plating the arms. Further, during the plating process, the arms are subject to acid baths to prepare the surfaces for plating. Before plating is commenced, the surfaces of the arms are rinsed in efforts to remove residual acid. In practice, it has been found that in spite of special efforts to rinse acid from within the lever arms, residual acid is retained by the scale and/or rust on those surfaces and is retained in the spaces between the arms and the plugs set therein. After the wrenches are finished, the residual acid attacks the materials of the arms and plugs and has been found to attack and react on all of the other elements and parts of the wrench within the arms, to do irreparable damage thereto.
The most satisfactoty way in which to reduce the adverse effect caused by residual acid within the lever arms of such wrenches has been to hone the interior surfaces thereof susequent to plating them. Such a procedure, in addition to being extremely costly, has not been fully effective since it has not effectively reached the spaces between the arms and their related plugs in which acid is commonly trapped and from which the acid eventually weeps.
In addition to the foregoing, in the noted common manufacturing procedures, where the internally threaded plugs are set in the lever arms at the time that the arms are plated, undesirable chrome is deposited in the threads of the plug and the threads must be suitably chased after the plating operation. This is but one more operation that must be performed and which adds to the cost of such wrenches.
While the above noted problem of being unable to establish and maintain the interiors of the lever arms of torque wrenches free of scale and rust might appear to be of secondary or minor significance, it is in fact a matter of great significance since those procedures which are practiced to reduce, but which fail to solve the problem, notably increase the cost of manufacture of the wrenches.
In accordance with the foregoing, it will be readily apparent that the cost of an adjustable click-type torque wrench can be materially reduced by eliminating any one or more machining and/or finishing operations that must be performed on the tubular metal lever arms thereof and that the effectivness, durability and therefore, the very utility of such wrenches can be notably enhanced and assured by a wrench structure which allows for quick, easy and economical cleaning and finishing of the interiors of the lever arms in the course of their manufacture.